The present invention relates to energy cells and, more particularly, to a system and method to facilitate voltage balancing in a multi-cell battery.
Various battery-powered devices employ multi-cell battery packs as power sources to energize associated electronics. The use of a pack of cells, rather than a single cell, can provide higher voltage delivery or greater capacity through increased amp-hours. However, the voltages on the individual cells tend to become unbalanced over time, such as during storage and/or usage, because each battery cell has its own distinct charging and discharging characteristics. The difference in voltages among cells in a battery pack creates an imbalance condition among the battery cells, which can lead to the loss of capacity in the battery pack. Accordingly, various cell balancing systems have been developed in an effort to balance the individual cells to help prevent overcharging as well as achieve uniform charging of all the battery cells.
Many conventional cell balance systems, for example, require relatively complex control circuitry to controls operation of the associated balancing system. The cell balancing system typically includes an array of sensors that monitor voltages in one or more cells of the battery pack. Further each cell can include its own associated monitoring and control circuit. Additionally, balancing often is achieved by discharging selected cells through a resistor. Therefore, the power requirements necessary to control and operate a conventional cell balancing system for a multi-cell battery pack can be significant. As the power requirements for the cell balancing system increase, the incremental benefits tend to decrease proportionally. Additionally, the overhead associated with the combination of components needed to implement most conventional systems increase the resulting cost of the battery pack or charging system.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
One aspect of the present invention provides a system for balancing electrical energy of a plurality of energy cells, such as can be connected to form part of a battery pack. The system includes a power transfer system that can connect to each of the battery cells to transfer energy between the connected cell and an associated storage device (e.g., a capacitor). The energy is transferred from the cell or associated storage device having a higher potential to the other storage device or cell having a lower potential. The connection can occur for a predetermined time period or it can be implemented for a duration sufficient to allow the relative potentials of the connected cell and storage device to become substantially equal.
Another aspect of the present invention provides a method for balancing electrical energy among a plurality of energy cells. The method includes repeatedly connecting and disconnecting each of the plurality of energy cells relative to an energy storage device. The method can continue indefinitely. Alternatively, the method can be terminated after the cells are sufficiently balanced and then reinitiated after the cells go imbalanced.